[test_dhcpv6_relay]: set DHCP server MAC address for packets send fro…

…m server's name (#4177)

Summary: fixed test_dhcpv6_relay - set src MAC address for DHCP reply packets

fixed DHCP server forged packets
Reply packets sent from DHCP server's name don't have MACs set and they don't come to DHCP client. Added src MACs for the packets and the packets now come to the client

ansible/roles/test/files/ptftests/dhcpv6_relay_test.py

@@ -230,6 +230,7 @@ def verify_relayed_solicit_relay_forward(self):
     def server_send_advertise_relay_reply(self):
         # Form and send DHCPv6 RELAY-REPLY encapsulating ADVERTISE packet
         advertise_relay_reply_packet = self.create_dhcp_advertise_relay_reply_packet()
+        advertise_relay_reply_packet.src = self.dataplane.get_mac(0, self.server_port_indices[0])
         testutils.send_packet(self, self.server_port_indices[0], advertise_relay_reply_packet)
 
     # Verify that the DHCPv6 ADVERTISE would be received by our simulated client
@@ -279,6 +280,7 @@ def verify_relayed_request_relay_forward(self):
     def server_send_reply_relay_reply(self):
         # Form and send DHCPv6 RELAY-REPLY encapsulating REPLY packet
         reply_relay_reply_packet = self.create_dhcp_reply_relay_reply_packet()
+        reply_relay_reply_packet.src = self.dataplane.get_mac(0, self.server_port_indices[0])
         testutils.send_packet(self, self.server_port_indices[0], reply_relay_reply_packet)
 
     # Verify that the DHCPv6 REPLY would be received by our simulated client